1. Field of the Invention
The present invention relates to an equalizer for a vestigial side-band (VSB) receiver, and more particularly, to an equalizer for a VSB receiver which compensates for VSB broadcast signal distortions occurring on transmission channels using field synchronization information which includes synchronization information on each field of a VSB broadcast signal and segment synchronization information including synchronization information on each data segment of the field.
2. Description of the Related Art
For broadcast signal transmission modes for digital broadcast implementations, there are currently a vestigial sideband (VSB) modulation mode and a coded orthogonal frequency division multiplexing (COFDM) modulation mode. The VSB modulation mode is a mode for broadcast signal transmissions in which a broadcast signal is transmitted on a single carrier. The COFDM modulation mode is a mode for broadcast signal transmissions in which a broadcast signal is transmitted through multiple transmission channels with multiple divisions of the broadcast signal. The VSB modulation mode is the digital broadcast transmission mode chosen by Korea, the United States of America, and so on. The COFDM modulation mode is the digital broadcast transmission mode chosen by Europe.
FIG. 1 is a block diagram schematically showing a conventional VSB transmitter. The VSB transmitter has a data inserter 11, an encoder 12, a multiplexer (MUX) 13, a pilot inserter 14, a modulator 15, and an RF-converter 16. The data inserter 11 interleaves the data to be transmitted to a receiver (shown in FIG. 2) according to a predetermined transforming method. The encoder 12 encodes the data interleaved in the data inserter 11. At this time, a generally used encoding method in the encoder 12 is the trellis encoding method.
The MUX 13 inserts field synchronization information F and segment synchronization information S in the encoded data according to a set method. The field synchronization information F includes mode information and the like together with field synchronization information. The segment synchronization information S includes synchronization information of each data segment within a field. Such field synchronization information F and segment synchronization information S are used when restoring data at the receiver.
The pilot inserter 14 inserts a pilot in a VSB broadcast signal including data, field synchronization information F, and segment synchronization information S output from the MUX 13. The modulator 15 applies the VSB modulation to the VSB broadcast signal which includes the pilot based on a set transmission mode. The RF-converter 16 high-frequency-modulates the VSB-modulated VSB broadcast signal for transmission to receivers through an antenna 18.
FIG. 2 is a block diagram for showing a general VSB receiver. The VSB receiver has a tuner 22, an IF amplifier 23, a synchronization detector 24, an offset restorer 25, an equalizer 26, a decoder 27, and a data extractor 28. The tuner 22 selects a desired bandwidth, based on a channel selection command, for the VSB broadcast signal transmitted to the VSB receiver and received at the antenna 21. The IF amplifier 23 IF-amplifies the received VSB broadcast signal of the desired bandwidth. The synchronization detector 24 converts the IF-amplified VSB broadcast signal into a digital format, and restores VSB broadcast signal carrier distortions occurring upon a channel selection operation of the tuner 22. The offset restorer 25 compensates for frequency, phase, and timing offsets as to the VSB broadcast signal which occur upon operations of the synchronization detector 24.
The equalizer 26 compensates channel distortions occurring at a transmission channel of the VSB broadcast signal output from the synchronization detector 24. The decoder 27 decodes data of the VSB broadcast equalized in the equalizer 26. The data extractor 28 carries out interleaving operations which combine data of a VSB broadcast signal interleaved in the VSB transmitter shown in FIG. 1.
FIG. 3 is a view showing a data frame structure of the VSB broadcast signal transmitted from the VSB transmitter shown in FIG. 1. Specifically, FIG. 3 shows one of the data frames of a VSB broadcast signal. One data frame is composed of two fields, a first field and a second field. Each field has 313 segments. The first and second fields each have the same kind of information, so only the first field is described as an example.
The first field is composed of data including a first field synchronization information F1, the segment synchronization information S, and Forward error correction (FEC), as error check information, which is encoded in the encoder 12. The first field synchronization information F1 includes synchronization information indicating a start of an input of the first field, and so on, and is composed of 828 symbols. The segment synchronization information includes synchronization information indicating a start of every segment, and so on, and each segment is composed of four symbols. A repetition period time is 77.3 μs per segment, and a repetition period time is 24.2 ms per field. Accordingly, a repetition period time of one data frame is 48.4 ms.
The equalizer 26 of a conventional VSB receiver uses a training sequence when equalizing data of the VSB broadcast signal so as to equalize the field synchronization information F included in a pre-set region of the field synchronization information F. Further, the equalizer 26 of the conventional VSB receiver uses the segment synchronization information S repeated at every segment to catch a start point of data included in a corresponding segment. Accordingly, the equalizer 26 of the conventional VSB receiver operates in training for equalizations while segment synchronizations are received.
However, the equalizer 26 of the conventional VSB receiver operates in a blind mode for equalizations while data of each segment is received. Accordingly, the equalizer 26 of the conventional VSB receiver, upon equalization operations, repeats the training and blind modes in one field at every segment. Therefore, the equalizer 26 of the conventional VSB receiver has a problem in frequent switching operations for equalization mode changes.
Further, the equalizer of the conventional VSB receiver has a problem in worsening its data equalization performance since the equalization is carried out in the blind mode when equalizing a section including data of each segment.